Laser testing: movement!

I just completed a new (much better) scanning head in preparation for final build and testing, but how do you know if the head is actually moving back and forth?

The answer I came up with is to use reflected laser light to amplify the movement of the scanning head.

To test the new head, I mounted a small mirror (actually a sequin, they’re lighter) in the needle mounting point, shined (shone?) a laser at the mirror to see if I could see movement in the reflected laser point as the scanning head moves back and forth. ¬†What I saw was a little movement, but the laser reflection was so diffuse and the movement was so much smaller than the laser reflection that the movement didn’t show well on the video I shot, so you’re going to have to put up with still photos until I acquire better mirrors and/or a more focused laser.

Laser and sequin

Diffuse, reflected laser light


3 Responses to “Laser testing: movement!”

  1. Oren Beck says:

    I used to service plotters that laser exposed microfilm for “blueprint” type documents.

    One hack I was taught on that gear was placing a black paper cover on the moving mirror so spot focus on the black paper showed up easily visible- if you are using a visible laser of course. since your project is- the trick may work for you. BtW- front surface vs back surface mirrors is an often overlooked friend or enemy in laser work. Things like that sequin are good for lowering moving mass, but less good for optical flatness. Though, the sequin may have some front surface value if that surface is not back painted.

  2. Tom says:


    I’ve been following this project with great interest and hope to see you pull it off soon, so thought I would throw in a suggestion for the laser setup you mention here.

    Using salvaged parts from an old DVD-writer would give you some fairly high grade and ultra light optical components. Using the mirrors + the grating unit would give you an easy way to detect the distance / movement since you only have to measure the distance between the 2 side-spots rather than trying to follow around the fuzzy beam on your living room wall :-)

    good luck on the project!


    • Sacha says:

      Thanks Tom, I’ll keep an eye out for a broken DVD writer and see what parts I can scavenge. Your idea of using grating to measure the movement sounds cool, I’ll see if I can google up some info on what I need to do.